For example, in the network field related to OA (Office Automation) apparatuses, Ethernet (registered trademark) establishes itself as a de facto standard communication system. On the other hand, in the field of FA systems, many kinds of communication systems are present as selectable communication systems. This is because, for example, FA systems involve various needs concerning function of a communication system, a type of wiring, convenience of the wiring, maximum wiring length, the number of connectable FA products, communication speed, performance of abnormality detection of communication, types of products adapted to the FA system, and the like and there are peculiar circumstances in which, because an FA system to which FA networks and FA products are applied often operates for a long period, it is not easy to change a communication system of a network.
For example, Patent Literature 1 discloses an example of an FA system in which networks in three hierarchies, i.e., a LAN (Local Area Network), a cell network, and a field network are used. For example, the LAN is used for communication between factories, the cell network is used for communication in a factory, and the field network is used for communication in manufacturing facilities in a factory. A communication system is sometimes different for each of the hierarchies. There are sometimes a plurality of options of a communication system in each of the hierarchies.